In the penguins' time, New Zealand itself was mostly underwater—only a smattering of islets were above the surface. Shallow waves rich with food and protection from predators would've made the habitat ideal for the birds.

Picturing the scene 25 million years ago, Ksepka sees an assortment of various penguins crowded onto remote, rocky outcrops—much like the areas inhabited by modern penguins in New Zealand, though the researcher imagines active volcanoes possibly turning prehistoric skies cloudy with ash.

In a hat tip to that ancient homeland, the team has named the species Kairuku waitaki and Kairuku grebneffi—"kairuku" roughly meaning "diver who returns with food" in the language of New Zealand's indigenous Maori people.

But "in New Zealand, where they have one of the peak areas for [giant penguin] diversity, they haven't been really fully described"—making the new reconstruction an important advance, said Clarke, whose work has been supported by the National Geographic Society's Expeditions Council. (The Society owns National Geographic News.)

Both of the new species lived alongside four other penguin species, each of which likely ate different fish prey—a level of local diversity rare today, study leader Ksepka noted.

"The fact they're five species all standing on the same beaches—it's pretty incredible," he said.